Collaborative Research: The Role of Iron Redox Dynamics in Carbon Losses from Tropical Forest Soils

了解碳和其他元素是如何在森林中转化的，对于维持和培育这一重要的全球自然资源至关重要。在热带森林中，这些变化可能会对气候变化做出反应，进而导致全球气候系统的反馈。特别是，潮湿的热带森林比地球上任何其他生态系统循环碳的速度都要快。持续温暖和潮湿的气候促进了植物的快速生长，以及死亡植物材料的快速分解。然而，在湿润、富含粘土的土壤中，生物活动消耗氧气的速度往往快于扩散的速度，这暂时在表层土壤中造成了氧气利用率低的地区。人们普遍认为，氧气供应不足的时期会减缓消耗枯死植物物质的微生物的活动，从而提高土壤碳储量。如果氧气供应波动，这可能会导致更复杂的相互作用。拟议的工作将有助于更好地理解这些联系，有助于解释为什么热带森林的土壤二氧化碳排放量是全球最高的，并为公共政策制定者使用的全球模型和预测提供信息。此外，该项目将教育和培训K-12学生，并向公众传播科学发现。项目负责人Silver博士将与波多黎各的当地合作者一起开发和举办关于传播气候变化科学的年度研讨会。这项研究将有助于更好地理解热带森林中碳循环的控制，方法是：(1)确定铁氧化还原循环在有机质分解中的作用；(2)量化热带森林中两个新的生物地球化学过程的重要性-非生物铁氧化与碳氧化耦合，以及增加铁氧化产生的溶解有机碳。这两个过程都有可能对生态系统的碳通量做出重大贡献，并改变我们对热带生态系统碳动态的理解。研究将采用实验室、现场实验和建模相结合的方法。实地实验将在波多黎各的Luquillo实验森林进行，并将利用作为国家科学基金会资助的临界区观测站一部分安装的自动传感器网络，以及将形成模板的相关研究，以进行铁和碳生物地球化学相互作用的实验。放射性碳测量将确定氧化碳的相对年龄，并将使用13C标记底物来探索铁氧化刺激复杂碳化合物分解的可能性。结构方程和动力学模型将使我们能够将工作扩展到生态系统层面。这项研究开发的概念和数值模型将解决微尺度氧化还原过程与生态系统层面的碳循环之间的缺失联系，涉及一系列森林土壤条件和景观位置。这项工作将有助于确定热带森林生物地球化学对气候变化和相关氧化还原条件的潜在敏感性，以及土壤碳动态对大气二氧化碳的反馈。

An understanding of how carbon and other elements are transformed in forests is critical to sustaining and nurturing this important global natural resource. In tropical forests, these transformations are likely to respond to variations in climate, and in turn, cause feedbacks in the global climate system. In particular, humid tropical forests cycle carbon more rapidly than any other ecosystem on Earth. A consistently warm and wet climate promotes rapid plant growth, as well as rapid decomposition of dead plant material. However, in their wet, clay-rich soils, biological activity frequently consumes oxygen faster than it is replaced by diffusion, temporarily creating regions of low oxygen availability in the surface soils. Periods of low oxygen availability are generally thought to enhance soil carbon storage by slowing the activity of micro-organisms that consume dead plant matter. If oxygen availability fluctuates, this may lead to more complex interactions. The proposed work will lead to a better understanding of these linkages, help explain why tropical forests have the highest global rates of soil carbon dioxide emissions, and inform global models and predictions used by public policy makers. In addition, the project will educate and train K-12 students and communicate scientific findings to the public. Project leader Dr. Silver will develop and run annual workshops on communicating climate change science together with local collaborators in Puerto Rico. Both PIs will provide direct student instruction including workshops with elementary students in California and internships for students from Georgia high schools with lower college attendance.This research will contribute to a better understanding of the controls on carbon cycling in tropical forests by: (1) determining the role of iron-redox cycling in organic matter decomposition; (2) quantifying the importance of two novel biogeochemical processes in tropical forests - abiotic iron oxidation coupled to carbon oxidation, and increased dissolved organic carbon production from iron oxidation. Both of these processes have the potential to contribute significantly to ecosystem carbon fluxes and to alter our understanding of carbon dynamics in tropical ecosystems. Studies will use a combination of laboratory, field experiments and modeling. Field experiments will be conducted in the Luquillo Experimental Forest, Puerto Rico, and will take advantage of an automated sensor network installed as part of the NSF-funded Critical Zone Observatory, as well as related research that will form the template from which to conduct experiments on the interactions of iron and carbon biogeochemistry. Radiocarbon measurements will determine the relative age of oxidized carbon, and 13C labeled substrates will be used to explore the potential for iron oxidation to stimulate the decomposition of complex carbon compounds. Structural equations and kinetic models will allow us to scale the work to the ecosystem level. The conceptual and numerical models developed from this research will address missing linkages between microscale redox processes to ecosystem level carbon cycling across a range of forest soil conditions and landscape positions. This work will help determine the potential sensitivity of tropical forest biogeochemistry to changes in climate and associated redox conditions, as well as feedbacks from soil carbon dynamics to atmospheric CO2.